This invention relates to yard and switching locomotives for relocation of train cars, and more particularly to a low speed locomotive having a simplified two axle design powered and suspension system which provides for increased traction, particularly at low speeds.
Switching or yard locomotives have been used since the invent of locomotives to perform the tasks associated with moving and relocating cars within a train switching yard, an industrial plant or a distribution center. These locomotives are designed for short distance pulling, moving and repositioning of train cars at relatively low speeds. They are required to operate at relatively large adhesion or traction forces starting from a stopped position to a transporting speed. A large portion of their time is spent connecting to, starting and stopping the train cars that are relocated from place to place. These switching locomotives must be designed to accomplish these tasks in an efficient cost effective manner.
Conventional switching locomotive designs of the present include a large diesel engine directly coupled to a direct current (DC) generator to convert the mechanical power into DC power. The DC power is supplied to a DC drive control cabinet that controls the amount of energy to two DC motors to convert electrical energy into mechanical energy at the wheels to drive the locomotive. A problem with the DC motor efficiency is observed at the very low end of the speed range where the static pulling force is large when the train is starting to move. The DC system efficiency at low speeds is commonly measured to be only about 50 percent. A separate alternator is also necessary to generate auxiliary AC power with this DC system. Conventional switching locomotives have four axles with two axles in each tractor portion of the locomotive. Each tractor is driven by a separate AC motor driving both axles. Weight transfer occurs when the locomotive is pulling or pushing the train cars. The weight transfers so that one axle is loaded more and the other axle is loaded less. The amount of traction provided by the wheels in contact with the rails depends on the normal force or weight of the wheels on the rail. When one axle is unloaded the DC drive control must adjust the output of the DC motor so that the wheels will not spin out of control. Therefore, two motors working at about 60 percent of their full rating is not uncommon. The two tractor system with four axles driven by two DC motors can become very inefficient. The DC generator size and the horsepower of the diesel engine must also compensate for the lower efficiency of the DC system. In addition, braking traction is generally not available using the DC motors of this conventional locomotive.
The two tractors of the conventional locomotive are also made to swivel with respect to the frame of the locomotive. This is necessary for the locomotive to be able to negotiate turns and keep the wheels in contact with the track. Each axle is sprung with respect to the tractor and the tractors are sprung with respect to the frame of the locomotive. The suspension and swivel systems with two tractors results in a number of expensive mechanical components which must be maintained and lubricated. In addition, the DC driven locomotive is relatively heavy and transporting the locomotive over long distances for use at another location is slow and generally must be accomplished by a rail system.
The need remains to solve the problems outlined above for the conventional switching locomotive. The problems of locomotive system efficiency, weight transfer and traction control between axles, added suspension maintenance and lubrication, transportation needs between use locations, auxiliary AC power, braking of the locomotive and an overall cost effective design are the subject of this invention; as disclosed in the following sections.
Accordingly, an object of the present invention is to provide a locomotive having an efficient and cost effective drive train system that provides traction control between drive axles.
Another object of the present invention is to provide an unsprung wheel/axle system supporting the locomotive so that controlled pitch and roll attitudes exist during various operations of the locomotive including driving and braking with various drive train systems.
Yet another object of the present invention is to simplify the suspension system and the number of necessary components between the frame of a locomotive and the unsprung wheel/axle system, while maintaining adequate ride comfort.
A further object of the present invention is to provide a locomotive that can be disassembled and shipped to a remote location using standard highway trucking means.
An additional object of the present invention is to provide a switching locomotive which is easy to operate in a safe manner at a reasonable switch engine speed, and requires little maintenance.